This invention relates to variable magnification optical assemblies used in scanning, electrographic type reproduction devices, in which assemblies a change in magnification is accomplished by repositioning half lenses or reflex lenses (called reflex lenses herein) so as to change the conjugate distances and thereby the magnifications for the assemblies.
Many optical assemblies are known for use in scanning type electrographic reproduction devices in which the magnification produced by the assembly between an image window and an object window can be changed. Generally the magnification produced by these assemblies is changed either by changing the focal length of a lens included in the assembly (e.g., by adding lens elements) or by changing the position of optical elements (typically mirrors and a lens within the assembly) to produce different paths through the device for light reflected from the document (called light paths herein), which different light paths have portions of different lengths (or different conjugate distances) between the object window and the lens and between the lens and the image window. The addition of lens elements avoids some potentially complex optical alignment problems, but is a relatively expensive approach. Assemblies for providing different light paths with different conjugate distances are usually less expensive but can be prone to alignment difficulties, particularly where reflex lenses are utilized to further reduce cost of the optical assembly. A reflex lens has a reflective surface on one side that is normal to its axis of the lens. The reflex lens must receive light traveling along a light path through the assembly at some angle to its axis (since light received along the axis of the lens would also be reflected back along the axis), and will reflect that received light back through the lens at an angle with respect to the incident light that is bisected by the axis of the lens. These angles of incidence and reflection must be taken into account when the lens is moved into different positions to ensure that the reflex lens will receive and reflect light in proper alignment with the other optical components defining the two light paths through the assembly.
U.S. Pat. No. 4,029,409 describes an optical assembly in which the magnification produced by the assembly between a fixed image window and a fixed object window on a housing for the assembly can be changed by changing the position of a reflex lens so that the reflex lens and cooperating mirrors in the assembly will provide two different light paths with different conjugate distances through the assembly between the windows. The reflex lens described in that patent, however, does not reflect light in the same direction along a common portion of the light paths toward the image window, and the two portions of the two light paths which are incident on the reflex lens at its two different positions are not parallel. Thus not only must the reflex lens be moved between its two positions, but it must also be pivoted so that it will properly align with the other elements defining the two light paths in each of its positions. Such pivoting of the lens must be precise, and such precise pivoting of the lens is difficult and costly to achieve and to maintain during the lifetime of the optical assembly.
U.S. Pat. No. 4,084,897 describes an optical assembly in which the magnification produced by the assembly between an image window and a fixed object window on a housing for the assembly can be changed by movement of a reflex lens so that the reflex lens and cooperating mirrors in the assembly will provide two different light paths with different conjugate distances through the assembly between the windows. In each of its positions the reflex lens reflects light in the same direction along a common portion of the light paths toward the object window and the two portions of the two light paths which are incident on the reflex lens at its two different positions are parallel. Thus the carriage need only be moved in a linear motion along the optical path of light reflected from the reflex lens and need not be pivoted as it is moved between its two positions, thus affording an optical assembly which is easier to align and maintain in alignment than the optical assembly described in U.S. Pat. No. 4,084,097. In the optical assembly described in U.S. Pat. No. 4,084,897, however, the parallel path portions for light incident on the reflex lens in its two positions are provided by changing the location of the object window, which change complicates both the illumination mechanism for the assembly and the mechanism for orienting an object to be copied with respect to the object window.